In this paper, molecular dynamic (MD) simulations are employed to characterize the liquid flow systems consisting of single- or multi-atoms as argon, water or ethane. These molecular flows are driven by various pressure gradients in nano-sized channels of different heights. The simulations find the existence of layer structures near the wall and the compressibility effect across the nano-sized channel for argon molecules. Slip velocity is obtained and the associated accommodation factor and laminar friction factor are varied with channel size in nano-scale. Furthermore, the flow characteristic in terms of velocity distribution inside nano-channels for different liquid molecules with multi-atoms exhibits very different transport phenomena. In conclusion, the inter-atomic interaction models between liquid atoms or liquid-solid atoms play important roles near interfaces in fluid transport of nano-sized channel flow.